Amplifiers are used in various applications. Among these applications, miniaturization is often very important for video and audio applications. In advanced integrated circuits, low supply voltage is used for reducing power consumption. However, for a real-world signal such as a voice signal, the amplitude may be larger than the supply voltage. Accordingly, in addition to a low-V amplification stage, another high-V amplification stage, which is coupled to a higher supply voltage, is required to provide a large signal.
FIG. 1 schematically illustrates a two stage dual supply amplifier, in which a low-V amplification stage 110 is coupled with a high-V amplification stage 140. In an example of a headphone application, a supply voltage VDD1 coupled to the low-V amplification stage 110 is about 3.3V, while a supply voltage VDD2 coupled to the high-V amplification stage 140 is about 8 to 12V. In such a structure, an inter-stage capacitor 120 is required to isolate the low-V amplification stage 110 and the high-V amplification stage 140. As known in this field, the capacitor occupies a large area in the integrated circuit. Therefore, such a circuit structure is costly and inefficient.